I think this is what you meant by:

... I had that from the Author Tools on the sidebar. It still shows the wrong URL.

Do this:

--- /scripts/alike03/Youtube_grey_out_watched/source@1.0+63356fa
+++ /scripts/alike03/Youtube_grey_out_watched/source
@@ -8,7 +8,7 @@
 // @icon        https://www.youtube.com/favicon.ico
 // @updateURL   https://openuserjs.org/meta/alike03/Youtube_grey_out_watched.meta.js
 // @supportURL  https://openuserjs.org/scripts/alike03/yt_grey_out/issues
-// @downloadURL https://openuserjs.org/src/scripts/alike03/yt_grey_out.user.js
+// @downloadURL https://openuserjs.org/src/scripts/alike03/Youtube_grey_out_watched.user.js
 // @copyright   2021, alike03 (https://openuserjs.org/users/alike03)
 //@license     MIT
 // ==/UserScript==

We always read in the current URL in your source that you have. So you need to click the Regenerate some keys from the current editor source button to correct your incorrect value. That's a reason why the button exists.

OUJS Admin